This project will continue and expand field studies of rhesus monkey populations in India, which were begun by the principal investigator in October 1959. Continuous census records of this population of rhesus monkeys have been obtained every year since 1959. The main sponsor of the program, the Johns Hopkins International Center for Medical Research and Training (under N.I.H. grant RO7-AI-10048-12) is moving to Bangladesh and Nepal, and cannot support work in India after 1973. The work involves field census of rhesus groups three times a year. The groups are natural, free-ranging groups in a rural agricultural area of approximately 300 square miles around the city of Aligarh, 80 miles southeast of New Delhi. Data will be obtained on group sizes, sex and age ratios, infant mortality, juvenile and adult losses, annual natality, annual production, and overall population trends. The data will provide a long-term assessment of population changes and dynamics in rhesus monkeys, and will be important in evaluating the supply of rhesus monkeys for biomedical research.